This style of rifles I'm sorry to say would be something that was never used by the military. Both on the USMC Unertl and also the A5.
To tell a little background, the A5 was pretty much considered obsolete even before WWI.
The Army actually had wanted a Goertz German Scope as their sniper scope in the early teens, but for obvious reasons it never happened with the start of the war. Frankford arsenal had the only optical shop in all the military, so they were ordered to copy the German scope design and make a functioning scope that could be mass produced.
Well Frankford came up short, so the design was turned over to WRA in 1917 to make the design work. That design of scope became known by WRA as the Model of 1918 scope.
That Model 0f 1918 scope was what the Army wanted as a sniper and they ordered tens of thousands of them. They were to be put on a modified sporterized Winchester Model 1917. That M1917 with that scope became the Model of 1918 Sniper. They only made a small amount for testing and they just couldn't handle the recoil and the scopes failed. As far as I know, none of these rifles or scopes still exist. The docs say they were destroyed in testing. But the war ended before the design could be fixed so this rifle never happened. This is the only M1917 sniper rifle platform that ever was to actually be made and fielded by the Army. There really wasn't any others past small numbers to test.
The Army did have WRA mount 900 A5 scopes on the M1903's supplied by them in 1918. This was because they couldn't get the Warner Swaseys in time with a shortage of kodak lenses for the scopes, and WRA did not have the bugs worked out on the Model of 1918 scope. These were the only A5 snipers used by the Army in WWI. There were never any M1917 snipers used by any branch. They were also identical to the 500 WRA mounted for the Marines in 1917. In total WRA made 1400 of these for the Army and Marines combined. These did not have the Mann Niedner tapered bases that you see confused with in all the books. These had a WRA base called the Springfield Marine. The bottom is a pic taken in France in about Jan 1918 of a WRA mounted rifle in the hands of a Marine.
The other style of A5 did have the tapered bases. It's unclear how many were for sure built by the Marines. It might have only been 150 during the war, but I could argue it either way. The Marine Philly Depot did for sure start to build them after the war and continued to build them as needed into WWII. These have the tapered blocks that have been modified to the existing WRA mounts. They work on a wedge design that tightens under recoil. The Marines also changed the micrometers to ones that were easier to read, but still quite confusing by later standards. This is a pic of a WWI Mann Niedner in france.
If you want to see them side by side to see the differences. The top one was built by WRA for the Army and Marines. The bottom is an WRA A5 scope modified by the Marines at the Philly depot to the tapered blocks and updated micrometers. This one pictured was actually built by the Marines in WWII. The Marines built at least a 150 of the Mann Niedners in 1941/42 for training, the Marine Raiders, and the Navy.
To the original question. The Marines got rid of all their M1917's by 1920. They never did any major testing of the Model 1917 as a sniper. They very much loved the M1903 and the M1917 was not see in the same affection by the Marines. I think I have a few mentions of them trialing some studies with the M1917, but it never made it past testing. The Marines did have M1917's and were going to switch over to it in the AEF, as everyone in the AEF was required to do so for logistics and such. But there is no evidence the Marines ever did any work on the M1917's as snipers past a handful of rifles. The Marines turned in all their M1917's by 1920, so there is no chance they ever built any with the Unertl 8X scopes.
The Army did not not have any real interest in building a M1917 sniper either. The only reason they considered it was Winchester could build the rifles and scopes together. But outside of that they had no interest in mounting A5 scopes to the M1917. They did do some testing with the M1917, mostly post WWI as a sniper rifle. But it never went anywhere.
The M1917 shown above with Mann Blocks and claims it was Marine. I honestly doubt it. It would require some documentation to back up the story. As the Mann Niedner tapered blocks were EXTREMELY common among competitive shooting. They were so common that many people and gunsmiths made and used those blocks. They were used on a lot of scoped rifles back in the day. I think personally that rifle is just a civilian made rifle.
But this is the same mistake I see so many experts in this field make. They find a vintage rifle that appears to show some USMC trait, and it has a scope, and it automatically becomes a sniper. This is the furthest from the truth. The Marines were not revolutionary or unique in their search of a sniper rifle. Most often they copied off the best commercial shooting designs of their time.
So sorry to say many sniper rifles I see traded, are just some commercial target rifle from back in the day. It's just the Marines liked to copy these commercial target rifles as many of the guys who built the sniper programs for the wars, were team shooters and they knew what worked and what was accurate.
The whole concept of the M1917 sniper is for the most part just something that was never really considered. So the rifle would be more a fantasy piece than anything in any configuration.
